In order to stabilize combustion and enhance fuel economy of an engine, a system is generally used for controlling the coolant temperature so as to be constant by bypassing a coolant passage from a radiator by opening and closing a thermostat valve.
Thermostat valves are known in which a channel to a radiator outlet passage is provided to an independent thermo element temperature-sensitive chamber on the engine outlet side, and the thermostat valve is actuated in a manner with the radiator outlet-side coolant temperature reflected too. A thermo wax which thermally expands is sealed in the then no element of the thermostat valve, and the valve body is opened and closed according to the coolant temperature. Furthermore, a Nichrome heater or other heating element coupled with the thermo element, and the valve body is opened and closed to electronically control the coolant temperature (see Patent Literature 1, for example).
Solenoid valves are also known which have a movable part that is urged in the closing direction by a spring. The valve is closed when a coil is not excited, and open when the coil is excited (see Patent Literature 2, for example).